Bulb coating method



April 29, 1958 v. VODICKA 2,832,694

BULB comma METHOD I Filed Sept. 22, 1954 FZI- 4 20 I 22 /8\ COMP.A|R v VAcuuM 2! 2! L2 La I w I 33 6 as Inventor:

Vincent VodicKa,

His Attorney States BULB COATING METHOD Vincent Vodicka, South Euclid, Ohio, assignor to General Electric Company, a corporation of New York Application September 22, 1954, Serial No. 457,668

4 Claims. (Cl. 117-33.5)

This invention relates to a method and apparatus for applying thin uniform coatings of powdered material to the concave inner sides of convex end faced lamp bulbs and similar articles.

In the production of electric lamps or other electrical devices embodying a bulb or envelope having a convex end face coated on its inner side with powdered material, such as a fluorescent powder or phosphor for instance, it has been difficult with prior known coating methods to produce a uniform coating of such powder material. Thus, with prior known coating methods wherein the coating is applied simply by introducing a predetermined quantity of a suspension of a coating material into the lower end of the bulb while in an inverted neckup position, followed by the suction withdrawal of the excess suspension from the bulb, a small pool of the coating suspension is generally left and collects at the center or lowermost region of the bulb end face. On drying, this pool of coating suspension then forms a local thickening in the coating, at the center of the bulb end face. Also, with such prior known coating methods the subsequent drainage of the wet coating material on the bulb end face toward the center or lowermost region thereof, results in a coating of non-uniform character which is relatively thin at the outer regions and progressively thicker toward the central region of the bulb end face. Such non-uniform coatings and local thickenings therein are not only detrimental to the apperance of the coated article but, in the case of a fluorescent lamp or similar device, are also detrimental to the efliciency thereof. Moreover where the coating material employed is of highly expensive character, such as is the case with certain special type phosphors, the prior known coating methods are wasteful of such expensive coating material due to the inability with such coating methods, of obtaining full recovery of all the excess of the coating material from the bulb.

It is an object of my invention, therefore, to provide a method of producing a coating of powdered material on the concave inner side of a convex end face portion of a lamp bulb or similar article to thereby provide a coating which is of uniform character and is substantially free of local thickenings.

Another object of my invention is to provide apparatus of simple construction, and easily operable, for producing a uniform coating of powdered material on the concave inner side of a convex end face portion of a lamp bulb or similar article.

Briefly stated, in accordance with one aspect of the invention, a suspension of the powdered coating material is first introduced into the bulb up to the desired cut-off level thereof, through a filling tube inserted into the bulb while in an inverted neck-up position, and then withdrawn from the bulb through the said filling tube by applying suction thereto. Immediately thereafter, the filling tube is removed from the bulb and the excess of the coating suspension which remains at and which has am I 2 drained to the center or lowermost region of the inverted bulb is then removed by suction into a relatively small size inner suction tube inserted all the way down into the inverted bulb, while a gentle current'of drying air is simultaneously created in the bulb flowing radially across its end face, through an air tube inserted in the bulb and surrounding the suction tube, to thereby promote the drying of and promptly set the wet coating on the bulb end face so as to minimize the settling or drainage of the wet coating toward the lowermost or central region of the bulb end face such as would otherwise result in a variation in the thickness of the coating from the center of the bulb end face to the outer regions thereof.

Further objects and advantages of my invention will appear from the following detailed description of a species thereof and from the accompanying drawing.

In the drawing,

Fig. 1 is a diagrammatic elevational view showing the first step of the coating method comprising my invention,

Fig. 4 is a view similar to Fig. 2 and illustrating another modification of the invention.

Referring to the drawing, the invention is there shown as applied to an electric lamp bulb 1 of glass or other suitable vitreous material having a single open-ended neck portion 2 and a convex bowl or end face portion 3, herein illustrated as of shallow dish shape, to the concave or inner side 4 of which a coating 5 (Fig. 2) of powderedmaterial is tobe applied. The coating 5 may consist of a fluorescent powder or phosphor such as is employed in fluorescent lamps, and it covers the concave inner side of the bulb end face 3 up to a predetermined given cut-off line 6 which, as shown,may be in the immediate vicinity of the maximum diameter of the bulb, at the junction between the convex end face portion 3 and the side wall portion 7 thereof.

In producing the coating 5 in accordance with the method of my invention, the bulb 1 to be coated is first positioned in an upright neck-up position as shown in Fig. 1 in a suitable holder 8. The bulb 1 is then filled with a suspension or slurry 9 of the powdered material,.

which may comprise a fluorescent powder or phosphor such as magnesium germanate for instance suspended in a suitable vehicle or liquid dispersion medium such as a solution of nitrocellulose or ethyl cellulose in butyl acetate and naphtha, may be supplied from a reservoir 12 thereof in a container 13 closed to the atmosphere. The filling tube lliextends down into the container 13, through the top Wall 14- thereof, a sufficient distance to maintain its lower end submerged within the reservoir 12 of coatingfl The coating suspension 12in the container 13 is forced into. the bulb 1 and subsequently withdrawn therefrom by first suspension at all times during the coating operation.

connecting the container 13 to a source of compressed air and thence to a source of vacuum. The compressed air or vacuum is supplied to the container 13 through a tube 15 which extends into the container and is connected Patented Apr. 29,1958

through a valve 16 either tothe source of compressed air or to the source of vacuum.

The suction withdrawal of the coating suspension 9 from the bulb 1, through the filling tube 10, is continued until all of the coating suspension in the bulb down to the level of the lower end 11 of the inserted filling tube 10, is withdrawn from the bulb. However, because of the fact that the filling tube It) is preferably made of large enough size to enable the introduction of the required amount of coating suspension into the bulb, and its subsequent withdrawal therefrom, in a reasonably short interval of time, and also because of the necessity for spacing the lower end 11 of thefilling tube to a slight distance above the inner side 4 of the bulb end face 3 so as to enable the egress of the coating suspension from the filling tube 10 and its subsequent ingress back into the filling tube, a small puddle or collection of the coating suspension, as indicated by the dotted line 17 in Fig. 1, remains at the center or lowermost region of the bulb end face 3. This excess or remaining collection of coating suspension at the center of the bulb end face 3 is also added to by the subsequent natural drainage of the wet coating material on the bulb end face 3 toward the center or lowermost region thereof, prior tothe setting and drying of the coating on the bulb end face. if the coated bulb were now allowed to dry while in such condition, without any further steps takento remove the puddle 17 of coating suspension at the vcenter of the bulb end face 3, a heavy center or local thickening would then be formed in the coating 5 on the bulb end face. Such a local thickening or heavy center in the coating 5 is not only detrimental to the appearance of the lamp bulb or other article, but in the case of a fluorescent lamp, is also detrimental to the efficiency thereof. Moreover, the natural drainage of the wet coating material on the concave inner side 4 of the bulb end face 3 toward the central or lowermost region thereof, which would occur during the relatively long period of time required for the wet coating to set and dry on the bulb end face, by natural air drying thereof, would cause a considerable variation in the thickness of the coating 5 from the center of the bulb end face outwardly to the outer regions thereof, the coating 5 being progressively thinner toward the said outer region. Such a variation in thickness of the coating 5 likewise would be objectionable in most cases as, for instance, in the case of a fluorescent lamp where it would be detrimental to lamp efiiciency.-

In accordance with the invention, therefore, immediately upon withdrawal of thecoating suspension 9 from the bulb 1 through the filling tube 10, the latter is withdrawn from the inverted bulb and suitable means 18 then inserted thereinto, as shown in Fig. 2, for not only withdrawing the pool of coating suspension 17 remaining and collected at the center of the bulb end face 3, but for also creating a gentle current of drying air directed radially across the wet coating on the bulb end face for the purpose of promoting the setting and drying of the wet coating so as to minimize the drainage thereof toward the central or lowermost region of the bulb end face such as would cause a variation in the thickness of the final dried coating 5 on the bulb end face. The means for accomplishing the above result comprises a combination suction and air current generating head composed of a pair of concentric tubes, i. e., an inner suction tube 19 connected at its upper end to a source of vacuum through a valve 20, and an outer air tube 21 adapted to be connected at its upper end through a valve 22 either to a source of vacuum as shown in Fig. 2, or to a source of compressed air as shown in-the modification of Fig. 3. The lower end of the inner or suction tube 19 is shaped in the form of a nozzle 23 having an intake orifice or opening 24 of relatively small size (of the order of 1 mm. in diameter, for instance) so as to enable the withdrawal into the suction tube 19 of substantially all the remainder 17 of coating suspension at the center of the bulb end face 3. For this purpose, the inner or suction tube 19 is positioned in the '4' bulb 1 with its nozzle end 23 practically in engagement with the center or lowermost portion of the bulb end face 3, as shown in Fig. 2.

The outer or air tube 21 is relatively large in size as compared to the inner tube 19 in order to provide an appreciable annular space therebetwcen (e. g., of the order of 5 mm. in width) so as to enable a large volume of air to be passed through the air tube 21, at relatively low velocity. As shown in Fig. 2., the air tube 21 is preferably separated from the inner or suction tube 19 by an intermediate tube 25 so as to provide an annular air intake opening 26 between the said tubes 21 and 25 at their lower ends. Also, as shown in Fig. 2, the outer or air tube 21 and the intermediate tube 25 terminate at their lower ends at approximately corresponding levels slightly above the lower or nozzle end 23 of the inner suction tube 19 so as to position the lower ends of the said tubes 21 and 25 (and therefore the air intake opening 26 therebetween) a slight distance above and spaced from the bulb end face 3 when the nozzle end 23 of the suction tube 19 is substantially in engagement with the bulb end face 3 during the use of the apparatus 18.

Upon insertion of the suction head 18 into and positioning thereof in place within the bulb 1 in the manner shown in Fig. 2, the valves 26 and 22 are opened so as to connect both the inner suction tube 19 and the outer air tube 21 to respective sources of vacuum. The suction in the inner tube 19 then draws up thcreinto the remaining quantity or pool 17 of coating suspension at the center of the bulb end face 3 while the suction in the outer or air tube 21 draws air into the open upper end of the bulb 1 so as to create a current of air in the bulb which, as it reaches the lower region of the bulb, flows radially inward of and across the wet coating 5 on the bulb end face 3, as shown by the arrows in Fig. 2, to thereby promote the drying of and promptly set the wet coating. The degree of vacuum supplied to the air tube 2-1 is so regulated by the valve 22 as to produce only a gentle air current in the bulb 1 across the wet coating 5 on the bulb end face 3 of insuificient velocity to disturb or ripple the wet coating. The vacuum connection to the outer or air tube 21, and the resulting flow of air into and through the bulb l, as continued at least until the wet coating 5 on the bulb end face 3 has sufficiently dried or set so as not to undergo any further drainage or settling thereof toward the lowermost or central region of the bulb end face. Meanwhile the vacuum connection to the inner suction tube 19' is maintained during the full period of time required for the wet coating on the bulb end face 3'to thus set sufficiently to'no longer drain to and collect in a pool at the center of the bulb end face 3,'in ordertothereby assure the continued withdrawal into the suction tube 19 of the excess coating suspension as it collects at the center of the bulb end face 3 during such time interval for the coating to set on the bulb end face. After the coating on the bulb end face 3 has set, the valve 22 is then closed to terminate the air current in the bulb and the vacuum supply valve 20 is also closed or left slightly open so as to assure the continued retention ofthe excess coating suspension drawn up thereinto, whereupon the suction head 18 is then removed from the bulb. The resultant coating 5 thus produced on the curved bulb end face 3 is not only of substantially uniform thickness throughout but is also substantially free of any local thickening or heavy center at the central region of the bulb end face 3.

In the modification shown in Fig. 3, the air tube 21 is connected at its upper end, through valve 22, to a low pressure source of compressed air instead of to a vacuum as in Fig. 2. In this modified arrangement, therefore, the air tube 21 directs a gentle stream of air into the bulb 1, at the lower or central region thereof, which is likewise effective to create a gentle flow of air in the bulb across the, wet coating 5 on the bulb end face 3 which then serves to promote the drying and setting of the said coating.

While it is preferred to employ an intermediate tube 25 disposed concentrically within the outer air tube 21 and separating it from the inner or suction tube 19, satisfactory results are nevertheless obtained with the intermediate tube 25 omitted as in Fig. 4. With this modified arrangement, the outer air tube 21 may be connected, through valve 22, either to a source of vacuum, as shown, or to a low pressure source of compressed air as in Fig. 3.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. The method of producing a uniform coating of powdered material on the concave inner side of the convex end face of a lamp bulb or similar article having a single neck end opening, which method comprises positioning the bulb with its open neck end up, introducing a suspension of the powdered coating material into the bulb, up to the desired cut-off level thereon, through a relatively large size filling tube inserted in the bulb, withdrawing as much as possible of the said suspension from the bulb through the said filling tube by applying suction thereto, removing said filling tube from the bulb, then immediately withdrawing substantially all the excess of said suspension remaining and collecting at the lowermost region of the bulb end face into a suction tube inserted in the bulb and having a relatively small diameter lower nozzle end while simultaneously creating a gentle current of air in the bulb, flowing across the coated end face of the openended bulb, through a relatively large size air tube inserted in the bulb with its lower end adjacent the bulb end face, and continuing both the said withdrawal of the said excess of suspension and the said air current in the bulb at least until the coating on the bulb end face is set.

2. The method substantially as set forth in claim 1 wherein the said current of air in the bulb is created by withdrawing the air from said bulb through said air tube.

3. The method substantially as set forth in claim 1 wherein the said current of air in the bulb is created by introducing compressed air into the bulb through said air tube.

4. The method of producing a uniform coating of powdered material on the concave inner side of the convex end face of a lamp bulb or similar article having a single neck end opening, which method comprises positioning the bulb with its open neck end up, introducing a suspension of the powdered coating material into the bulb, up to the desired cut-ofli level thereon, through a relatively large size filling tube inserted in the bulb, withdrawing as much as possible of the said suspension from the bulb through the said filling tube by applying suction thereto, I

removing said filling tube from the bulb, then immediately withdrawing substantially all the excess of said suspension remaining and collecting at the lowermost region of the bulb end face into an inner suction tube inserted in the bulb and having a relatively small diameter lower nozzle end while simultaneously creating a gentle current of air in the bulb, flowing radially inwardly across the coated end face of the bulb, by withdrawing the air from the bulb through a relatively large size outer suction tube surrounding said inner suction tube and having its lower end located adjacent the end face of the bulb, and continuing both the said withdrawal of the said excess of suspension and the said air current in the bulb at least until the coating on the bulb end face is set.

Birdseye et al Aug. 24, 1943 Leet et al July 6, 1948 

1. THE METHOD OF PRODUCING A UNIFORM COATING OF POWDERED MATERIAL ON THE CONCAVE INNER SIDE OF THE CONVEX END FACE OF A LAMP BULB OR SIMILAR ARTICLE HAVING A SINGLE NECK END OPENING, WHICH METHOD COMPRISES POSITIONING THE BULB WITH ITS OPEN NECK END UP, INTRODUCING A SUSPENSION OF THE POWDERED COATILNG MATERIAL INTO THE BULB UP TO THE DESIRED CUT-OFF LEVEL THEREON, THROUGH A RELATIVELY LARGE SIZE FILLING TUBE INSERTED IN THE BULB, WITHDRAWING AS MUCH AS POSSIBLE OF THE SAID SUSPENSION FROM THE BULB THROUGH THE SAID FILLING TUBE BY APPLYING SUCTION THERETO, REMOVING SAID FILLING TUBE FROM THE BULB, THEN IMMEDIATELY WITHDRAWING SUBSTANTIALLY ALL THE EXCESS OF SAID SUSPENSION REMAINING AND COLLECTING AT THE LOWERMOST REGION OF THE BULB END FACE INTO A SUCTION TUBE INSERTED IN THE BULB AND HAVING A RELATIVELY SMALL DIAMETER LOWER NOZZLE END WHILE SIMULTANEOUSLY CREATING A GENTLE CURRENT OF AIR IN THE BULB, FLOWING ACROSS THE COATED END FACE OF THE OPENENDED BULB, THROUGH A RELATIVELY LARGE SIZE AIR TUBE INSERTED IN THE BULB WITH ITS LOWER END ADJACENT THE BULB END FACE, AND CONTINUING BOTH THE SAID WITHDRAWAL OF THE SAID EXCESS OF SUSPENSION AND THE SAID AIR CURRENT IN THE BULB AT LEAST UNTIL THE COATING ON THE BULB END FACE IS SET. 